const object1 = {name: 'Tu', hobbies: 'coding'}

copyAndCreateNewObject = (prevObj, key, value) => {
  const obj = {}
  for (let k in prevObj) {
    obj[k] = prevObj[k]
  }
  obj[key] = value
  return obj
}

console.log(copyAndCreateNewObject(object1, 'age', 31))
// { name: 'Tu', hobbies: 'coding', age: 31 }